Hendra virus

Hendra virus

Posted 30/08/2011 by Roger Beckmann

Hendra virus is in the news again. In the last month, the disease has struck in the Gold Coast hinterland and again in northern New South Wales. The Queensland and New South Wales governments have provided additional funding of $6 million over three years for further research.

Hendra virus can live in horses, bats, humans and, as recent events have demonstrated, dogs. This is a nasty virus. About 70% of horses who get the disease will die from it. Of even more concern is the fact that it has also proved fatal to people. Where did it come from, and what can be done about it? It seems that the virus probably originated in ‘flying foxes’ (also known as fruit bats). These animals don’t show signs of illness when they are infected, which suggests that they have adapted to the virus over time. When the virus enters a completely different host – such as horses or people – it can cause severe illness and death. Although not yet proved conclusively, it seems likely that horses acquire the virus from bats. The virus is present in the urine, faeces, blood, and amniotic fluid of bats. When these find their way onto whatever the horse is eating, there is a possibility of infection. Infected horses will release the virus in nasal secretions, urine and saliva, but the virus doesn’t travel in exhaled air. Virus release can happen before obvious symptoms are present, and will continue during the course of the disease. In this way, other horses nearby can become infected.

Transmission to humans can also occur by means of contact with horse secretions. However, this route is not easy. In the seventeen years since the disease appeared, many people have had contact with infected horses without getting sick. Just seven people are known to have become infected with the virus in this time; tragically, four of these have died, including the first known human case in 1994. It is possible that dogs can get infected from close contact with infected horses. The dog that was known to be infected had tested positive to antibodies but showed no outward sign of sickness.

Queensland DPI reports that laboratory studies have shown that other species including cats, guinea pigs, ferrets and pigs can all develop disease when injected with Hendra virus in an experimental setting. Rabbits and dogs developed antibodies to Hendra virus in an experimental setting, but did not develop any signs of illness. The likelihood of virus transmission in a real world situation, however, is not the same as being injected with the virus in a lab.

There is no cure for the disease in either humans or horses and, so far, no commercial vaccine to prevent it. However, CSIRO’s Australian Animal Health Laboratory (AAHL) is working on a vaccine for horses which should be available for field trials in 2012.

Unique to AustraliaThe virus has not been reported from anywhere else in the world. It was completely unknown until 1994, when a ‘mystery’ disease appeared in some horses in Brisbane. AAHL subsequently isolated the virus and identified it, naming it Hendra after the Brisbane suburb where it first appeared. Initially the disease was known as equine morbillivirus, until further research revealed the nature of the virus. The disease is not the same as, or related to, equine influenza. AAHL has developed a diagnostic kit for the disease, so the virus can be accurately identified in infected animals.

Is a bat cull required?Some people have suggested that flying foxes should be culled to prevent further outbreaks of this disease. The Queensland Department of Primary Industries and Fisheries argues against this. They point out that flying foxes are widespread in Australia and, as they are highly mobile, it is not feasible to cull them all. And culling or dispersing flying foxes in one location could simply transfer the issue elsewhere. Furthermore, flying foxes are a protected species and play an important environmental role, as they pollinate native trees and spread seeds.

Experts consider it unlikely that bats could transmit the disease directly to humans. There has been no recorded case of transmission in that way, and there is no evidence that it can occur. Equally, however, there is no evidence that would absolutely rule it out. However, it would require ingesting something contaminated with bat urine, faeces or blood. Hendra is not a highly infectious virus; it appears to require more than just casual exposure.

Handling fruit bats, however, is not a good idea as they can also carry lyssavirus and it is known that they can infect humans with this. But that's another story.

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